This is education, not advice
The information here is written for the general reader and does not replace a personal medical consultation. It cannot tell you what is producing the difference between your own breasts, or whether an operation is appropriate for your health or your circumstances.
A difference may be a diagnostic question first
A difference that is new, that is changing, or that comes with a lump, skin change or nipple discharge is assessed as a diagnostic problem before any surgical planning. Nothing on this site should be used to decide that such a finding can wait for a cosmetic consultation.
No outcome is guaranteed
No treatment can be guaranteed, and symmetry least of all. How the two sides heal, how an implant settles, how a lift matures and how much residual difference remains vary between individuals, and the result is judged honestly at around a year rather than in the first weeks.
Scars are permanent
Breast surgery leaves permanent scars, and a plan that lifts one side and augments the other leaves scars of two different kinds. They mature and soften over a year or more, they do not disappear, and no surgeon can promise that they will be inconspicuous.